Phase modulation receiver



M. GQCROSBY 2,101,703 PHASE MODULATIO N RECEIVER Dec. 7, 1937.

Original Filed Jan. 23, 1932 3 Sheets-Sheet l CARR/ER SOURCE LEAMPUF/EkAND LIMIT-ER 0 1407041147 IC' V01 l/ME (047ROL CARR/ER I Hi. TER

CARR/ER AMPUFIER AND l/M/TER 0? AUTOMATIC VOZUMF 60/V7'k0l INVENTORMURRAY CROSBY ATTORNEY Dec. 7, 1937. G CROSBY 2,101,703

PHASE MODULATION RECEIVER 3 Sheets-Sheet 2 I Original Filed Jan. 25,1932 INVENTOR MURR CROSBY BY *5? ATTORNEY Dec. 7, 1937. M. e. CROSBY2,101,703

PHASE MODULATION RECEIVER Original Filed -Jan. 23, 1932 3 Sheets-Sheet 311 4 36 36 40 '32 if 34 msoamcr v POWER MUlT/PUER AMPl/F/ER I l j 4P/MSFMflDUMIOk CARR/ERUM/TER 0/-' FIGURE! 0R AUTOMATIC V01 l/Mf C0/V7k0lB c 0 v E IIHERWYNE CARR/ER j PHASE RECEIVER FILTER ADJUSTER {I EAMPl/F/ER AND CAM/5k LIM/TE/Z lIM/7Ek0R/ll/TOM477C 0/94070444776 VON/MEcameo:

VOLUME CONT/UL AMPL IFIEK V INVENTOR MURRAY G. CROSBY I BY ATTORNEYPatented Dec. 7, i937 7 t is 2,101,703 7 UNITED STATES PATENT OFFICE"PHASE MODULATION RECEIVER MurrayG. Crosby, Riverhead N. Y., assignor toRadio Corporation of America,- a corporation of Delaware 7 Originalapplication January 23, 1932, Serial No.

588,309, now Patent No'.2,081;577,"dated May 7 25, 1937. Diyided'andthis application Octoher 1, 1936, Serial 'No.'103, 505 V 6 Claims. (01.est-20) This invention relates to the signalling art and multiplied bythe order of the harmonic, or order pertains especially to thetransmission of intelof frequency multiplication. ligencefrom onegeographicallyseparated point. Another general object of my presentinvento another by the useof phase'modulated waves 'tion is to provideimproved reception methods or carrier energy and is a divisionof'Crosby. and means for phase modulated waves. United Statesapplication #588,309 filed January A further object of my invention isto provide 23, 1932, Patent No. 2,081,577,May 25, 1937. i a receivingsystem wherein the collectedphase' An object of my present invention isto promodulated energy is' combined in predetermined vide a new anduseful system for producinga phase relationship with energy ofsubstantially phasemodulated wave of substantially constant constantfrequency and phase and wherein the 10 frequency and, briefly, to do soI provide an arcombined. energies are then detected and trans rangementand a method wherein two voltages 'lated. It is desirable, of course, tohave the of substantially like frequency are combined less energycombined with the received energy in than 180 degrees-or any multiple of180 degrees exact synchronism with the received carrier out of phase toproduce a resultant voltage. energy; To provide for such energy, Iseparate According to my invention, further, the relative the carrierenergy f the received e e y n phase of the resultant voltage is variedby varying combine it in proper phase as will be explained the relativevalues of the voltages combined with o ful y hereinafter With all Of ereceived the predetermined number of degrees, out of energy whereby thecombined energy is in aform 20 phase. r which may be detected to givethe transmitted 20" 1 As' such procedure may introduce a certain si c ramount of amplitude modulation in the resultant It is a further obje Ofy invention to utilize phase modulated wave, which of course isunheterodyning at y receiver for phase medulated desirable, it is afurther object of my present in waves, using preferably a localheterodyne oscilvention to eliminate the amplitude modulation l r f a lefr q e y, a f rx mp 25- component. To do so the resultant phasemoduusing a cry eentrelled'eseilletor With p lated energy is limited by,for example, electron able crystals o difierent fundamental q dischargedevices operated at their saturation cies'. a point, to substantiallyconstant value. 'By heterodyning to the intermediate frequency Morespecifically, according to my present init is possible to'have all ofthe intermediate frevention, I carry out the foregoing objects by q y ap n and the final detector i applying to a pair of electron dischargedevices Qu s tu ed o e fi eq y 80 that O ly e voltages of like frequencya predetermined numtuning 'of the circuits ahead of the first detectorber of degrees out of phase such that the phase and the frequency of thefirst beating oscillator difference is not 0, 180 or any whole multiplerequires adjustment f u i e ss of 189 although phase differences varyingslightgr t y facilitates the tuning Operations a d 1y from 0, 180 etc.,are suitable. The outputs makes it possible to apply complicated filteror of the devices are so combined that there is a, crystal circuits inthe final stages of the receiver resultant voltage of like frequency, Tovary'the Which o d be e p if it W necessary 40 phase of this resultantvoltage, or, in other words, to ke t e eq y V b i the phase of theresultant carrier energy, I vary Th s f h hctcrodync pr pl ls makeoppositely the internal 'impedances of the elecit p ss toobtein energyfrom the final d tron discharge devices. Preferably, I apply mdt'ectorcircuits which :varies when the transmitter ulating voltages toscreen grids of the devices frequ c or receiver oscillator varies, whichv and carriervoltages out of phase to other energy C be11ti1iZet0e0htr01 the frequency electrodes of the devices as will beexplained more of t fi t beating oscillator in aimanncr to pfullyvhereinafter. the receiver automatically tuned in to the de- Asdescribed, a' maximum shift of less than s d Sighelr r ispossible withthe foregoing'arrangement. Moreover, for Short Wave reception the o Toaugment still further the phase shift produced q y band f h h q n y sages is much by the modulating energy is a further object greater thanthe band of frequencies occupied by of my present invention. To do so,according thesignal with its sidebands. This excessively to myinvention, the phase shifted energy is wide frequency band allows noiseto enterthe frequency multiplied asa result of which the receiver; Byheating or heterodynlng down to Q5. frequencymultiplied output has aphase shift an intermediate frequency and there applying additionalfrequency selectivity it is possible to limit the frequency band of thereceiver to the band occupied by the signal. This results in minimumnoise and interference.

Further, in connection with heterodyning it may be noted that the firstheterodyne detector in a superheterodyne receiver serves the function ofsubtracting from all of the incoming frequencies, a frequency equal tothat of the first beating oscillator. If an incoming signal of, say10,000,000 cycles is modulated at the rate of 1,000 cycles with eitherphase or amplitude modulation, there will be produced sidebands 1,000cycles above and 1,000 cycles below the carrier. In this case thesesidebands have a spacing from the carrier of only 0.01% which is muchtoo small to permit ordinary circuits to discriminate between carrierand sidebands in the manner required for detection of phase modulation.If the signal with the 10,000,000 cycle carrier is beat with a firstoscillator having a frequency of, say, 9,900,000 cycles, I obtain anintermediate frequency of 100,000 cycles, which contains the sidebandsstill spaced 1,000 cycles from the carrier or an amount now equal to 1%.This separation is sufiiciently great so that two band pass filters maybe utilized to separate the sidebands from one another in the mannerdescribed in the copending application of C. W. Hansel], Serial #611,050filed May 13, 1932, Patent No. 1,999,902 granted April 30, 1935, and mycopending application, Serial #565,005 filed September 25, 1931 and itis also suificient to allow the carrier to be taken out through, forexample, a crystal filter, separately amplified and reintroduced withadjusted phase as described more fully hereinafter.

It may seem that, since at the transmitter, increasing the frequencyincreases the phase shift, at the receiver decreasing the frequency byheterodyning should decrease the shift. However, this is not so sincethere are two different processes involved. At the transmitter thefrequency is raised by frequency multiplying and at the receiver it islowered by heterodyning. When a Wave is frequency multiplied it ispassed into a harmonic generator and a harmonic is chosen for themultiplied output. Thus, only integral values of multiplication may beobtained corresponding to the 2nd, 3rd, 4th, etc., harmonics.

When this sort of multiplying is applied to a wave the phase orfrequency shift of phase or frequency modulation is multiplied by theorder of multiplication; that is, 2, 3, 4, etc. Thus, a 10,000 cyclewave frequency modulated by a 1,000 cycle shift has a 3,000 cycle shiftwhen it is multiplied to 30,000 cycles. The same amount ofmultiplication is obtained in phase modulation.

As required by law, my present invention is defined with particularityin the appended claims. However, it may best be explained both as to itsstructural organization and. mode of operation by referring to theaccompanying drawings wherein:

Figure 1 is a. wiring diagram of a phase modulation transmitting system,according to my present invention.

Figures 2 and 3 are vector diagrams given in order to explain theoperation of the system shown in Figure 1.

Figure 4 is a block diagram of a phase modulating system wherein thephase of a transmitted carrier may be shifted to an angle greater thandegrees.

Figure 5 illustrates one form of receiver, built in accordance with theprinciples of my present invention, for receiving and translating aphase modulated wave.

Figures 6 and 7 and 7a are vector diagrams explanatory of the operationof the receiving arrangement shown in Figure 5.

Figure 8 is a modified form of phase modulation receiver according to mypresent invention.

Figures 9 and 10 are vector diagrams explanatory of the operation of thereceiver of Figure 8.

Turning to Figure 1, illustrating a transmitter for transmitting phasemodulated energy, carrier energy or potentials from an oscillationgenerator 2 are fed to an artificial transmission line 4, terminated bya resistance that is equal in value to the surge impedance or resistanceof the line 4. The generator 2 may be a crystal controlled oscillator,or any other form of substantially constant frequency oscillationgenerator. By virtue of the termination of the loaded line 4, at thedesired carrier frequency, only travelling Waves appear in the inductiveportion 8 of line 4.

The control electrodes or grids I0, I2 of electron discharge devices I4,I6 are tapped through blocking condensers I8, 20 to points 22, 24 atinductance coil 8 which are less than apart, for example, 90.Accordingly, voltages of the same or like carrier frequency from source2 are fed to tubes I4, I6, 90 apart.

The vectorial relationship of the voltages so fed is illustrated inFigure 2 for the particular case of 90 degrees separation where Eaillustrates the voltage applied to tube I4 and Eb indicates thealternating voltage applied to tube I 6. Consequently in the outputcircuit I8 of tubes I4, I 6 there appears voltage Er as shown in Figure2. This is a resultant voltage which is of like frequency to the voltageapplied from source 2.

Carrier source 2, of course, for the purpose of obtaining voltages adesired number of degrees apart to be applied to the two electrondischarge devices I4, I 5 may take the form of two alternatorsmechanically tied together so that they can generate voltages 90, or anyother desired number of degrees apart in which case the output of eachalternator would be fed across the grid and cathode of one of the tubes.Or, the transmission line for obtaining voltages of predetermined phasedisplacement may be replaced by a network of resistances, inductancesand capacities to which energy of constant frequency is fed, each tubebeing coupled to portions of the network which have voltages generatedthereacross the desired number of degrees out of phase.

By oppositely varying the output of each of the two electron dischargedevices I4, IS the resultant may be made to receive any phase as shownin Figure 3 from vector Er to E: as indicated. This shift in phase isaccomplished by relatively decreasing the amplified voltage Ea,appearing in the output circuit due to the amplifier action of tube I4and relatively increasing amplified voltage Eb from tube I6 appearing inthe output circuit and vice versa.

In order to cause this opposite variation in voltages in tubes I 4, I0,modulation energy from a suitable source 24 and amplified by push-pullamplifier 25 is fed as indicated in opposite phase to the screen grids28, 30 of tubes I4, I6. sequently, the internal impedance of the twotubes is varied oppositely and, as a result, their outputs are variedinversely to their internal impedances, thereby causing a phase shift ofthe Con-' phase modulated energy so I appearing in the output circuitiii of electron ception of power amplifier .The output of the phasemodulator may be fed discharge devices 5-, I6 may then be amplified by asuitable amplifier 32 and radiated or propagated through space in theform of electromag-' 'netic wave energy by means of a suitable antennaM.

As will be evident from an inspection of Figure 3, thegreatest amount ofphase shift pos-. far described is a value sible with the scheme so lessthanlSO degrees, or with 90 degrees phase displaced voltages, 90degrees; and it is also evident that this arrangement introduces a smallmodulation. To eliminate the amplitude modulation the power amplifieramount of amplitude 32 should be operated at all times to its saturationpoint. ative amount of phase modulation, the apparatus 32 should includealso some form of frequency multiplier; V 7

Such an arrangement is shown diagrammatically in Figure 4 whereinrectanglefifi indicates all of the apparatus of Figure 1 with the ex- 32and antenna 34.

to a harmonic generator or frequency increaser dt which, bymultiplication in frequency of the output of apparatus 3 will cause anincreased phase shift in the multiplied frequency energy correspondingto the order of its harmonic, or order of frequency multiplication. 7

To eliminate amplitude modulation introduced by either the phasemodulation or the frequency multiplication, the frequency multiplier isfollowed by a limiter ill-whose output, in turn, is fed to poweramplifier 32. If desired, the lim- 7 iters may be placed ahead of thefrequency multiplier, or, limiters may be used both ahead of and behindthe frequency multiplier.

Figure 5 illustrates a system for receiving, tecting and translatingelectromagnetic waves propagated by 'a transmitter such as described inFigures 1 and 4. Propagated energy is col- 42 and beat to a suitableband of intermediate frequencies by the action of heterodyning apparatus44 of known construction including a variable frequency heterodyingoscillator variable so that signals over a wide range of frequencies maybe received. The intermediate frequency energy so derived is amplifiedto a constant value by the action of intermediate frequency amplifierand limiter 46. A portion of the energy of the intermediate frequencyband is fed to filter 48 which filters out energy only of the carrierfrequency and is fed to a carrier amplifier and limiter 5B.

The remaining portion of the intermediate frequency energy is fed toelectron discharge devices 52 through the action of transformer 54. Thelimited carrier frequency energy, however, is fed through a phaseadjusting device .56 and transformer 58 to the input side of theelectron discharge device 60 whose anode is connected as shown inparallel with electron discharge device 52. The phase adjusting device56 is so adjusted that the potentials fed to tube 60 are substantially90 degrees out of phase to the potentials fed to tube 52 as indicated inFigure 6 wherein Es illustrates vectorially a potential fed to tube 52and E0 indicates the potential fed to tube 60.

Now, with the reception of a non-modulated wave, the output of detector62 will be substantially constant as a result of which no sound willsecondary of transformer To increase or augment the rel-'- grids of thedetectors 8!], 82, 180

been modulated 'in accordance with signals reducing the frequency ofsaid amplitude limited 64. However, asa phase modulated wave is'rewillbe present in 66. Consequently, detector 62 will, throughtheintermediary of low frequency amplifier produce sound in the during thereception of phase modulatedsignals for the arrangement shown in Figure5 is given in Figures '7 and 7a., the-resultant 'electromotive force E'rfed to the control electrode of detector E2, varying, of course, withthe phase shift of the phase modulated'wave E. Of course, the sameresult may be obtained by feeding energy from a synchronously run localoscillator to the 54 or the primary 'of 58 rather than use the carrierapparatus, 50, 56, 58, Bil. However, the arrangement'shown is.preferable in view of the known difficulties of synchronously operatinga local oscillator.

Moreover, it is to be clear that heterodyning lation receiver, is notessential.

end, amplifiers M, 46 take than passing the mean frequency of anintermediate band 'of frequencies'pas'ses the mean frequency of thereceived radio frequency: band.

Another desirable form of receiving apparatus is shown'in Figure 8. lfrequency energy is fed to the control electrodes of detector tubes 80.82 cophasally as shownby the vectors E5 in Figures 9 and 10, whilefiltered carrier, energy is fed to the control electrodes or out ofphase, as shown by the vectors E0 of Figures 9 and. 10. Amplitudevariations characteristic of the phase variations and of the signalmodulations will be produced in the anode circuit energy.

I claim:

1. In a phase modulation signalling system the method of demodulatingcarrier wave energy the phase of which has been modulated in accordancewith signals which includes the steps of, collectsaid wave energy to alower frequency to increase the percentage of frequency spread be-'tween the carrier and sideband energy of said lower frequency, limitingthe amplitude of said wave energy of lower frequency, producingunmodulated energy characteristic of said carrier of said lowerfrequency limiting the amplitude of said produced unmodulated energy andcombining said limited unmodulated energy with amplitude limitedsideband energy of said lower frequency in substantially phasequadrature relation to produce resultant energy characteristic of thephase modulations on said collected energy.

2. The method of demodulating high frequency oscillatory energy thephase of which has which includes the steps of, limiting the amplitudeof said phase modulated oscillatory energy,

oscillatory energy and simultaneously increasing the degree of phasemodulation thereon to thereby produce characteristic energy of lowerfrequency, producing oscillatory energy characteristic of the carrierwave of said energy of reduced frequency limiting the amplitude of saidproduced oscillatory energy, separating said produced amplitude limitedoscillatory energy into be heard in the transmitting device or phonestransmitting device or ear. phones E i. An instantaneous vectorialdiagram:

As indicated, intermediate two portions of opposed phase, combiningamplitude limiter connecting said input electrodes to tude limitedsideband energy of said reduced said filter a. circuit connecting saidintermediate frequency wuth both of said portions in substan frequencyamplifier to said input electrodes, and tially phase quadrature, anddifferentially coma phase adjuster in one of said last two circuits. 5bining the resultants produced by said first com- 5. Means fordemodulating wave energy modu- 5 bining steps to produce a resultantwhich varies lated in phase at signal frequency comprising a inamplitude in accordance with the phase modupair of electron dischar e dvi es e ch hav n an lations on said oscillatory energy. anode, a cathodeand a control grid, an output 3. The method of demodulating oscillatoryencircuit connecting the anodes of said tubes in ergy modulated in phaseat signal frequency push-pull relation, an input circuit connecting 10which includes the steps of, reducing said oscilthe control grids ofsaid tubes in parallel, an latory energy to a lower frequency andsimulinput circuit connecting the control grids of said taneouslyincreasing the degree of phase tubes in push-pull relation, waveamplitude limmodulation of said oscillatory energy of reduced itingmeans for impressing said wave energy on frequency, limiting theamplitude of said energy one of said input circuits, and wave amplitude15 of reduced frequency, separating a portion of limiting and phaseadjusting means for impressthe energy of said reduced frequency andreing oscillatory energy characteristic of the carmoving therefrom allphase deviations, and imrier frequency only of said wave energy on thepressing said energy from which the phase deviaother of said inputcircuits. tions have been removed on energy of said re- 6. In a. systemfor demodulating oscillatory enduced frequency in substantially phasequadraergy modulated in phase, a pair of electron ture to produce aresultant characteristic of discharge devices each having a controlgrid, phase modulations on said energy. an anode and a cathode, anoutput circuit cou- 4. In a system for demodulating phase modupling saidanodes together, separate input cirintermediate frequency amplifier andamplitude odes of said devices, Wave amplitude limiting limiter, afilter coupled to said intermediate fremeans for impressing phasemodulated Wave enquency amplifier and amplitude limiter, said filterergy on one of said input circuits, and wave ambeing tuned to thefrequency of the carrier passed plitude limiting and phase adjustingmeans for by said intermediate frequency amplifier and amimpressingenergy characteristic of the carrier plitude limiter, a pair of electrondischarge deonly of said phase modulated wave energy on the vices havinginput electrodes and output elecother of said input circuits.

trodes, an indicating circuit connected with said output electrodes acircuit including an ampli- MURRAY G. CROSBY.

' lated energy, a heterodyne receiver including an cuits connected withthe control grids and cath- 25,

